Covalently attaching substituents to hydroxyl polymers, for example hydroxyethyl, hydroxypropyl, and methyl, is well known as a way to modify various properties of the hydroxyl polymer including solubility, viscosity, film formation, suspension of solids, and adhesiveness. Substituents which have carboxyl groups, for example carboxymethyl, can have additional properties including emulsion stabilization, binding of cationic species, crystal growth inhibition, and increasing the compatibility with other polymers. The carboxyl group can also be used to crosslink the hydroxyl polymer either by formation of ester links or by ionic crosslinks between carboxyl groups. Such crosslinked hydroxyl polymers can swell rapidly in water to form strong hydrogels. Substituents which are linked to the hydroxyl polymer via an ether linkage, for example carboxymethyl, hydroxyethyl, hydroxypropyl, and methyl are advantageous since the ether linkage is stable under both acidic and basic pH conditions. Ethersuccinate is a substituent which contains both carboxyl groups and an ether linkage to the hydroxyl polymer.
Synthesis of substituted hydroxyl polymers can be problematic. For example synthesis of carboxymethyl starch in the granular form requires either a high content of salt in the reaction mixture or the use of solvents in combination with water. The salt, solvents, and unreacted chloroacetate must be removed for many applications. In the case of hydroxyethyl starch, the reactor must have expensive safety controls due to the toxicity and flammability of the ethylene oxide reactant.
Accordingly, there is a need for substituted hydroxyl polymers which can be made with simple, inexpensive processes and which exhibit the various properties of substituted hydroxyl polymers, especially the property of being polymer processed in order to make various polymeric structures such as fibers, films, foams, and coatings.